Glossary

A1 and A2 amoeboid modes: Two fast ways of moving shown by cells squeezed onto non-adhesive surfaces: A1 cells keep a round body and push out a small front, whereas A2 cells are elongated, led by a large bleb and trailed by a uropod, with the cortex flowing rearwards (Liu et al. 2015). A2 is often treated as the same thing as stable-bleb and leader-bleb migration (Ullo & Logue 2018). First use found: Liu et al. 2015. “The first type, which we named A1”

Also written: A1 mode, A2 mode, amoeboid-1, amoeboid-2, A2 blebbing, fast amoeboid migration

See also stable bleb, leader bleb, confinement, uropod, cortical flow, amoeboid. Milestones: M20

Abercrombie steps of migration: A description of cell crawling as a repeating cycle of steps, drawn from Abercrombie's studies of fibroblasts on flat surfaces: the front extends, attaches to the substrate and pulls, and the rear lets go and is drawn forward (SenGupta et al. 2021). Some versions begin with the cell polarizing (García-Arcos et al. 2024, Trends Cell Biol ◆). In living cells the steps overlap in time, and whether they describe migration in 3D or by blebs is an open question.

Also written: Abercrombie cycle, cell motility cycle, four-step crawling cycle, multistep model of migration, Abercrombie-style model

See also lamellipodium, cell polarity, friction (active and passive), bleb-based migration, adhesion-independent migration, uropod. Milestones: M19

actin turnover: The continual exchange of actin between the filaments of the cortex and the pool of free actin in the cytoplasm, through which the cortex renews itself within seconds to tens of seconds even when it looks unchanged (Fritzsche et al. 2013; Chugh et al. 2018). It is usually measured by bleaching fluorescent actin in a small area and timing the recovery of fluorescence (FRAP), and given as a half-time or a rate.

Also written: cortical turnover, cortex turnover, cortex turnover time, F-actin turnover, FRAP half-time

See also cortex, cortex assembly, bleb cycle, cortical flow, stable bleb. Milestones: M13, M20

active gel: A network of cross-linked filaments that generates stress from within, because the motor proteins in it consume chemical energy; the actomyosin cortex can be described as one. The term names both a continuum theory used to model the cortex (Tinevez et al. 2009) and purified actin–myosin networks studied in vitro (Alvarado et al. 2013). First use found: Paluch et al. 2005. “Our observations suggest a mechanism based on active gel dynamics”

Also written: active gel theory, contractile active gel, active matter

See also percolation, solation–contraction coupling, cortex, cortical flow, reconstitution. Milestones: M06, M12, M15

adhesion-independent migration: Cell movement without specific adhesion molecules, such as integrins, gripping the surroundings. Force is transmitted instead by non-specific friction between a rearward-flowing cortex and the surroundings, or by the cell pushing against confining walls (Ruprecht et al. 2015; Bergert et al. 2015). First use found: Friedl et al. 2001. “Such ‘adhesion-independent’ locomotion, however, requires bilateral interaction”

Also written: adhesion-free migration, friction-based migration, non-specific friction, chimneying

See also confinement, cortical flow, stable bleb, A1 and A2 amoeboid modes, bleb-based migration, friction (active and passive). Milestones: M09, M19, M20

amoeboid: Moving in the manner of an amoeba. Today the word names a family of migration modes of rounded, weakly adherent cells that advance by blebs or by actin-driven pseudopods rather than by lamellipodia anchored by focal adhesions (Stuelten et al. 2018); which cells count as amoeboid 'remains vague and can also depend on the authors' (García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Lieberkühn 1854. “sich bewegende und nicht bewegende amöbenartige Körperchen”

Also written: amoeboid movement, amoeboid migration, ameboid, amœboid, amoebenartig (German), amoeboid mode

See also pseudopod, bleb-based migration, mesenchymal–amoeboid transition, A1 and A2 amoeboid modes, protoplasm. Milestones: M01, M02, M04, M11, M18, M20

apoptopodia: Long, thin, string-like protrusions made by apoptotic (dying) cells, with blebs at their tips (Poon et al. 2014) or, in the beaded form, a row of beads along them (Atkin-Smith et al. 2015). The blebs or beads can break off as apoptotic bodies. First use found: Poon et al. 2014. “which we preliminarily denote ‘apoptopodia’”

Also written: apoptopodium, beaded apoptopodia, beads-on-a-string, string-like protrusions

See also apoptotic body, apoptotic bleb, extracellular vesicle. Milestones: M17

apoptotic bleb: A bleb formed by a cell dying by apoptosis, during the execution phase. In the cell lines studied, caspase-3 cleaves and so activates the kinase ROCK I, which drives the actomyosin contraction behind the blebs (Coleman et al. 2001; Sebbagh et al. 2001); blebbing precedes the formation of apoptotic bodies (Mills et al. 1998). First use found: Pitzer et al. 1996. “their accumulation in apoptotic blebs during programmed cell death”

Also written: apoptotic membrane blebbing, apoptotic blebs

See also apoptotic body, apoptopodia, dynamic bleb, Rho–ROCK, blebbing, zeiosis. Milestones: M11, M17

apoptotic body: A membrane-bounded piece of an apoptotic cell, with or without nuclear material, that other cells take up (Kerr et al. 1972). It can form from detached blebs, from beaded apoptopodia or by phagocytes splitting the dying cell; which route dominates in tissues is an open question (M17). First use found: Kerr et al. 1972. “we shall call them apoptotic bodies”

Also written: apoptotic bodies, Councilman-like bodies (earlier name), apoptotic fragment

See also apoptotic bleb, apoptopodia, extracellular vesicle, cytoplast. Milestones: M11, M17

balloon: A descriptive word, not a technical term, for a large, thin-walled, fluid-filled protrusion or vesicle. Today it mostly describes the shape of stable-bleb cells (Ruprecht et al. 2015). First use found: Hogue 1919. “transparent, balloon-like structures were noted”

Also written: balloon-like structure, ballooning, balloons of cytoplasm, balloon-like shape

See also bleb, blister, bubble, stable bleb. Milestones: M03, M07, M20

bleb: A rounded bulge of the plasma membrane that forms where the membrane comes away from the actin cortex beneath it, or where the cortex breaks. Pressure inside the cell, generated by contraction of the cortex, inflates it; a new cortex then assembles under the bulge, which usually retracts (Charras & Paluch 2008; Tinevez et al. 2009). First use found: Ryder 1894. “small blebs or pseudopodial warts”

Also written: blebs, membrane bleb, bleb-like protrusion, zeiotic bleb, pseudopodial wart (1894)

See also blebbing, bleb cycle, stable bleb, nuclear bleb, inverse bleb, hernia, blister, zeiosis. Milestones: M03, M07, M08, M10, M12, M15, M19, M20

bleb cycle: The life of a single bleb: it starts by membrane–cortex detachment or cortex rupture, grows as cytoplasm flows in, stops growing as a new cortex assembles under its membrane, and retracts as myosin contracts that cortex (Charras et al. 2006; Tinevez et al. 2009). A transient bleb completes the cycle in about a minute (García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Dornfeld & Owczarzak 1958. “continuous protrusion and retraction of ectoplasmic blebs”

Also written: life cycle of a bleb, bleb nucleation, bleb initiation, bleb expansion, bleb growth, bleb retraction

See also bleb, rupture vs detachment, cortex, ERM proteins, blebbing regimes, cortex assembly, cortex scar. Milestones: M04, M07, M10, M12, M13

bleb-based migration: Cell migration in which blebs, rather than protrusions pushed out by actin polymerization, advance the front of the cell. It needs a contractile cortex and some grip on the surroundings, by adhesion or friction (Charras & Paluch 2008; Bergert et al. 2015). First use found: Johnson 1976. “Circus movements and blebbing locomotion in dissociated embryonic cells”

Also written: blebbing locomotion, bleb-based motility, blebbing motility, rounded bleb-associated mode, bleb-driven migration

See also amoeboid, stable bleb, leader bleb, circus movement, adhesion-independent migration. Milestones: M09, M11, M18, M19, M20

blebbing: The making of blebs by a cell, often many in succession over its surface. The word covers blebs in migration, division, spreading and cell death alike (Charras & Paluch 2008). First use found: Gay 1956. “exhibit a blebbing of the nuclear membrane”

Also written: bleb formation, cellular blebbing, membrane blebbing, surface blebbing

See also bleb, blebbing regimes, nuclear bleb, apoptotic bleb, dynamic bleb. Milestones: M07, M08, M11

blebbing regimes: A classification of blebbing by how long blebs last and how they behave: transient blebs retract within about a minute, circus blebs travel round the cell edge as a wave of membrane–cortex detachment, and stable blebs last for hours (García-Arcos et al. 2024, Trends Cell Biol ◆). The regimes differ mainly in how much cortex re-forms under the bleb front: all of it in transient blebs, part of it in circus blebs and none at the tip of a stable bleb. First use found: García-Arcos et al. 2024 (Trends Cell Biol) ◆. “which we refer to as ‘blebbing regimes’”

Also written: transient blebs, circus blebs, stable blebs

See also stable bleb, circus movement, bleb cycle, dynamic bleb, cortex scar. Milestones: M20

blebbisome: A large extracellular vesicle without a nucleus (mean diameters about 9–15 µm) that contains organelles such as mitochondria and keeps blebbing for days after its release. It forms when a retracting part of a cell stays tethered by a membrane nanotube that is then severed (Jeppesen et al. 2025). First use found: Jeppesen et al. 2025. “Blebbisomes are large, organelle-rich extracellular vesicles”

Also written: blebbisomes

See also extracellular vesicle, large oncosome, microvesicle, cytoplast. Milestones: M17

blebbistatin: A small-molecule inhibitor of non-muscle myosin II, named because it stops blebbing (Anonymous 2002). It is widely used to test whether a bleb-driven process needs myosin activity (e.g. Liu et al. 2015). First use found: Anonymous (JCB news staff) 2002. “The second inhibitor, called blebbistatin, is specific for nonmuscle myosin II”

See also myosin II, Rho–ROCK, cortical tension. Milestones: M12, M15, M18, M20

blister: An older, now occasional word for a bleb-like lifting of the plasma membrane. Some authors keep it for large protrusions of injured cells that do not retract (Cunningham 1995), and reconstitution papers use it for a different, inward protrusion into a liposome (Sakamoto et al. 2023). First use found: Chambers & Reznikoff 1926. “raises the plasmalemma locally in the form of a blister”

Also written: hyaline blister, blistering, potocytosis, Blasen (German)

See also bleb, bubble, hernia, balloon, dynamic bleb. Milestones: M03, M04, M10

bubble: A descriptive word, mostly of the 1950s–1970s, for blebs formed repeatedly over the whole surface of a cell, especially a dividing one ('bubbling'). It became rare after the 1970s, until a preprint revived it for a class of small, short-lived blebs (Lian et al. 2020 preprint). First use found: Goldacre & Lorch 1950. “This was reminiscent of the ‘bubbling’ which occurs”

Also written: bubbling, surface bubbling, cellular bubbling, anaphase bubbling

See also bleb, zeiosis, blister, balloon. Milestones: M07, M08

cell polarity: The organization of a whole cell into two different ends, with cytoskeleton, signaling molecules and organelles unevenly distributed between them. In a migrating cell, front–rear polarity sets the direction of movement; in blebbing cells it restricts blebs to the front, for example through weaker membrane–cortex attachment or stronger myosin contraction there (García-Arcos et al. 2024, Trends Cell Biol ◆).

Also written: front–rear polarity, polarisation, polarization, symmetry breaking, spontaneous polarisation, polarised blebbing

See also Abercrombie steps of migration, cortical flow, membrane–cortex attachment, ERM proteins, stable bleb, leader bleb, uropod. Milestones: M18, M19, M20

circus movement: Blebbing in which one bleb, or a wave of membrane–cortex detachment, travels round the edge of a round, non-adherent cell (Charras et al. 2008). Behind the wave the re-formed cortex, rich in myosin II, contracts and keeps the pressure high, driving detachment ahead of it; the wave may circle the cell without moving it or, if limited to the front, carry it forward (García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Pantin 1923. “described as a ‘circus movement’ by Loeb”

Also written: circus movements, circus bleb, travelling bleb

See also blebbing regimes, lobopodium, bleb, membrane–cortex attachment. Milestones: M13, M18

clasmatocyte and clasmatosis: Ranvier's names for large connective-tissue cells that shed pieces of their cytoplasm (clasmatocytes) and for the shedding itself (clasmatose), which he inferred from fixed membranes (Ranvier 1890). The cells were later equated with tissue macrophages (Krishnan et al. 1932), and 'clasmatosis' now also names the fragmentation of the cytoplasm of circulating tumor cells (Perea Paizal et al. 2021). First use found: Ranvier 1890. “Je donne le nom de clasmatocytes”

Also written: clasmatocytes, clasmatose (French), clasmatosis, CTC clasmatosis

See also merotomy, cytoplast, microvesicle. Milestones: M17

confinement: Mechanical restriction of a cell between surfaces or in narrow spaces: under a coverslip, a PDMS roof or agarose, in channels or in dense matrix. Combined with low adhesion, it switches many cell types to bleb-based migration (Liu et al. 2015; Logue et al. 2015; Bergert et al. 2015). First use found: Charras & Paluch 2008. “When the cell is in a confined environment”

Also written: confined migration, under-agarose assay, microchannel, chimneying

See also stable bleb, leader bleb, A1 and A2 amoeboid modes, adhesion-independent migration, nuclear bleb. Milestones: M19, M20

constriction ring: A narrow waist, lined by cortical actin, between the body of a moving cell and its leading protrusion or bleb; cytoplasm passes through it into the front (Haston & Shields 1984; Keller & Eggli 1998). First use found: De Bruyn 1946. “the occurrence of ‘constriction rings’ in moving leukocytes”

Also written: restriction ring, bleb neck, contraction wave

See also leader bleb, uropod, bleb. Milestones: M09, M10

cortex: The thin meshwork of actin filaments, myosin II motors and cross-linking proteins that lies just under the plasma membrane, a fraction of a micrometer thick (M13). Its contraction sets the tension of the cell surface, and blebs form where it comes away from the membrane or breaks (Charras & Paluch 2008; Tinevez et al. 2009). First use found: Schultze 1861. “eine oft ansehnlich breite Rindenschicht”

Also written: actin cortex, cell cortex, actomyosin cortex, cortical actin, Rindenschicht (German), cortical layer

See also cortical tension, membrane–cortex attachment, ectoplasm and endoplasm, plasmagel and plasmasol, cortical flow, cortex assembly, cortical contractility, actin turnover. Milestones: M02, M04, M06, M08, M10, M12, M13

cortex assembly: The building of new cortex on a patch of plasma membrane, where actin and its partner proteins are added faster than they are lost. Under a growing bleb, the bare membrane gains a new cortex in a set order in the cells studied, linkers such as ezrin first, then actin with early cross-linkers, then myosin II; this stops the bleb's growth and lets it retract (Charras et al. 2006; M13).

Also written: cortex reassembly, cortex re-formation, cortex reformation, de novo cortex assembly, bleb cortex

See also bleb cycle, cortex, actin turnover, ERM proteins, myosin II, cortex scar, blebbing regimes. Milestones: M06, M13, M20

cortex scar: The old cortex left behind where a bleb starts: as the membrane moves away, the original cortex stays at the bleb base and disassembles over seconds to tens of seconds while a new cortex forms under the bleb membrane (Zatulovskiy et al. 2014; Asante-Asamani et al. 2024). Each transient bleb leaves one (García-Arcos et al. 2024, Trends Cell Biol ◆), and a scar is a common sign that a protrusion is a bleb rather than an actin-driven pseudopod. First use found: Hagmann et al. 1999. “After completion of the retraction phase, a ‘scar’ of accumulated actin”

Also written: actin scar, F-actin scar, cortex scars, old cortex

See also bleb cycle, cortex assembly, blebbing regimes, pseudopod, rupture vs detachment, cortex. Milestones: M13, M18, M19

cortical contractility: How strongly the cortex tends to contract, a tendency generated mostly by myosin II motors pulling on its actin filaments. It is the main source of cortical tension and, through it, of the pressure that inflates blebs; high contractility favors blebs over lamellipodia (García-Arcos et al. 2024, Trends Cell Biol ◆).

Also written: contractility, cortex contractility, cortical contraction

See also myosin II, cortical tension, Rho–ROCK, intracellular pressure, cortex, blebbistatin, active gel. Milestones: M02, M06, M08, M11, M19, M20

cortical flow: Movement of the actomyosin cortex along the cell surface, parallel to the membrane, toward regions where it contracts more strongly. In migrating cells it runs opposite to the direction of movement and is also called retrograde flow; in stable-bleb cells this rearward flow, coupled to the surroundings by friction, propels the cell (Liu et al. 2015; Ruprecht et al. 2015; Bergert et al. 2015). First use found: Grębecki 1990. “continuous steady contraction producing centripetal cortical flow”

Also written: retrograde cortical flow, cortex flow, actomyosin flow

See also adhesion-independent migration, stable bleb, percolation, active gel, tail contraction and frontal contraction, friction (active and passive), cell polarity. Milestones: M06, M10, M20

cortical tension: The tension within the plane of the cortex, generated mainly by myosin II pulling on actin filaments. Together with membrane tension it sets the pressure inside the cell that drives blebs (Tinevez et al. 2009). First use found: Schroeder 1972. “a general relaxation of cortical tension has occurred”

Also written: cortex tension, apparent surface tension, threshold tension

See also cortex, intracellular pressure, Laplace's law, membrane tension, surface tension theory, cortical contractility. Milestones: M06, M12

cytokineplast: A motile piece of a cell without a nucleus that has broken away carrying the machinery for movement. The word was coined for the heat-released leading edge of neutrophils (Malawista & de Boisfleury Chevance 1982) and is now also used for detached stable blebs (García-Arcos et al. 2024, Dev Cell ◆). First use found: Malawista & de Boisfleury Chevance 1982. “We propose the name cytokineplast”

Also written: cytokineplasts, CKP, motile cytoplast

See also cytoplast, microplast, stable bleb, lamellipodium. Milestones: M17

cytoplasmic streaming: Bulk flow of cytoplasm inside a cell. In amoeboid movement it is the forward flow of the fluid inner cytoplasm (endoplasm) into an advancing pseudopod or bleb (Allen & Roslansky 1959; Charras & Paluch 2008). First use found: Schultze 1863. “das lebhafteste Spiel der Körnchenströmung”

Also written: protoplasmic streaming, Körnchenströmung (German, granule streaming), endoplasmic streaming, fountain streaming

See also tail contraction and frontal contraction, plasmagel and plasmasol, poroelasticity, hyaline cap. Milestones: M02, M04, M05, M12

cytoplast: A membrane-bounded piece of cytoplasm without a nucleus, made in the laboratory by enucleation or shed by cells, that can still move and bleb (Albrecht-Buehler 1980; Headley et al. 2016). The nucleated remainder is called the karyoplast (Roos et al. 1983). First use found: Wigler & Weinstein 1975. “enucleated cells, or cytoplasts”

Also written: karyoplast (the nucleated remainder), nucleoplast, enucleated cell, cell fragment, anucleate fragment, motile fragment

See also microplast, cytokineplast, merotomy, clasmatocyte and clasmatosis, extra-ovate, blebbisome. Milestones: M02, M17, M20

dynamic bleb: A bleb that grows and retracts on a healthy cell with an intact cortex, as opposed to the blebs of dying or injured cells (Weems et al. 2023). First use found: Cunningham 1995. “These blisters would be distinguished from the dynamic blebs”

Also written: non-apoptotic bleb, transient bleb

See also apoptotic bleb, blister, bleb cycle, blebbing regimes, septin signaling hub. Milestones: M08, M10, M16

ectoplasm and endoplasm: Classical names for the clear, firmer outer layer of cytoplasm (ectoplasm) and the granular, more fluid inner cytoplasm (endoplasm) of amoebae and other cells (Hyman 1917; Pollard & Ito 1970). In current terms they correspond roughly to the cortex and the bulk cytoplasm (our reading). First use found: Wallich 1863. “differentiated into ‘endosarc’ and ‘ectosarc’”

Also written: ectosarc, endosarc, hyaline ectoplasm, granular endoplasm

See also plasmagel and plasmasol, hyaline layer, cortex, hyaloplasm and granuloplasm. Milestones: M02, M04, M05, M08

ERM proteins: Ezrin, radixin and moesin, related proteins that, once activated by phosphorylation, bind both the plasma membrane and actin and so tie the membrane to the cortex. Their activity sets membrane–cortex attachment, and ezrin is among the first proteins to reach a retracting bleb (Charras et al. 2006; Diz-Muñoz et al. 2010). First use found: Priddle et al. 1998. “the ERM family of proteins that also act as linkers”

Also written: ezrin, radixin, moesin, ERM family

See also membrane–cortex attachment, bleb cycle, cortex, cortex assembly, cell polarity. Milestones: M11, M13, M15

extra-ovate: Loeb's name for the ball of protoplasm pushed out of a sea-urchin egg when its membrane burst in diluted sea water; it rounded up and could develop into an embryo (Loeb 1894, 1895). Historical only. First use found: Loeb 1894. “which was connected with the extra-ovate”

Also written: extraovate

See also cytoplast, merotomy, bleb, intracellular pressure. Milestones: M03

extracellular vesicle: The umbrella term for membrane-bounded particles released by cells, from exosomes (30–100 nm) and microvesicles (100–1,000 nm) to larger particles such as large oncosomes (Minciacchi et al. 2015). First use found: Schiera et al. 2007. “secrete them at least in part by shedding extracellular vesicles”

Also written: EV, large EV, ectosome, exosome

See also microvesicle, large oncosome, apoptotic body, blebbisome. Milestones: M17

Flory network theory: A polymer theory of gelation, after Flory, that predicts how much cross-linker is needed before filaments join into one network spanning the whole sample. Cell biologists applied it to actin gels between 1979 and 1993 (Hartwig & Stossel 1979; Pollard et al. 1982; Janson & Taylor 1993). First use found: Hartwig & Stossel 1979. “occur abruptly at a critical ratio of cross-linker to polymer”

Also written: Flory theory, Flory gel point

See also gelation, percolation, solation–contraction coupling. Milestones: M06

friction (active and passive): A force that arises where two surfaces slide past each other and opposes their relative motion; for a migrating cell, where its surface slides or rolls over its surroundings. Friction that couples a rearward-flowing cortex to the surroundings pushes the cell forward (active friction, or traction), while friction on parts that are dragged along, such as a uropod, holds it back (passive friction, or drag) (Liu et al. 2015). The cell advances when the first matches or exceeds the second. First use found: Liu et al. 2015. “The coupling of the actin retrograde flow to the substrate (active friction)”

Also written: friction, active friction, passive friction, traction, drag, friction coefficient, frictional support

See also adhesion-independent migration, cortical flow, uropod, stable bleb, A1 and A2 amoeboid modes, confinement, Abercrombie steps of migration. Milestones: M15, M18, M19, M20

gelation: The change of a solution of filaments into a connected, solid-like network (a gel). The gel point, or critical gelling concentration, is the concentration of cross-linker (or of filament) at which a network spanning the whole sample first forms (Pollard et al. 1982; Janson & Taylor 1993). First use found: Mast & Root 1916. “gelation pressure, absorption pressure, adhesion, cohesion, diffusion”

Also written: gel point, critical gelling concentration, gel state, gelling

See also sol–gel transformation, Flory network theory, percolation, solation–contraction coupling, plasmagel and plasmasol. Milestones: M04, M06

hernia: A protrusion of cell contents through a weak spot in an enclosing layer. Today the word appears mainly in definitions of blebs, as 'herniations of the plasma membrane', and of nuclear protrusions (Tinevez et al. 2009; García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Dujardin 1835. “une sorte de hernie momentanée”

Also written: herniation, hernie (French), Bruchsack (German, hernial sac), hernia-like protrusion, herniation of endoplasm

See also bleb, zeiosis, nuclear bleb, rupture vs detachment. Milestones: M02, M04, M08

hyaline cap: The clear (hyaline), granule-free zone at the tip of an advancing pseudopod of large amoebae, where the flowing endoplasm stops short of the membrane (Mast 1926; Allen & Roslansky 1958). The term is occasionally used for the clear front of blebs (Keller et al. 2002). First use found: Mast 1926. “as the plasmasol flows into the hyaline cap it spreads freely”

Also written: cap of hyaline ectoplasm, hyaline caps

See also hyaline layer, hyaloplasm and granuloplasm, tail contraction and frontal contraction, plasmagel and plasmasol. Milestones: M04, M05, M18

hyaline layer: A clear layer without granules at the surface or front of an amoeboid cell, visible by light microscopy (Schultze 1863). In blebs, it is the zone that is at first free of actin and organelles (Keller et al. 2002). First use found: Schultze 1861. “die hyaline Grundsubstanz eine oft ansehnlich breite Rindenschicht bildet”

Also written: hyaline margin, hyaliner Saum (German, hyaline seam), hyaline border, hyaline veil, hyaline ectoplasm

See also hyaline cap, hyaloplasm and granuloplasm, ectoplasm and endoplasm, cortex. Milestones: M02, M04

hyaloplasm and granuloplasm: Older names for the clear, fluid ground substance of the cytoplasm (hyaloplasm) and its granule-rich part (granuloplasm). 'Hyaloplasm' is still used occasionally for the fluid that fills a young bleb (Keller et al. 2002). First use found: Anonymous 1891. “the more fluid or hyaloplasm”

Also written: hyaloplasm, granuloplasm, spongioplasm

See also hyaline layer, hyaline cap, protoplasm. Milestones: M03, M04

intracellular pressure: The amount by which the hydrostatic pressure inside a cell exceeds the pressure outside. It is generated by the contracting cortex and inflates blebs; Laplace's law relates it to cortical tension and curvature (Charras et al. 2008; Tinevez et al. 2009). First use found: Hogue 1919. “until the pressure became so great that it elongated”

Also written: hydrostatic pressure, internal pressure, cytoplasmic pressure, turgidity

See also Laplace's law, poroelasticity, cortical tension, bleb, inverse bleb. Milestones: M04, M05, M07, M12, M14

inverse bleb: A bleb that grows into the cell instead of out of it. Where the pressure outside (of blood or intercellular fluid) is higher than inside, the membrane bulges inwards without actin and is then pulled back by actomyosin (Gebala et al. 2016; Schliffka et al. 2024). First use found: Gebala et al. 2016. “in a process that we termed inverse blebbing”

Also written: inverse membrane blebbing, inverse blebbing

See also bleb, intracellular pressure, hernia. Milestones: M14

lamellipodium: A flat, sheet-like protrusion at the front of adherent cells, pushed forward by a growing network of branched actin filaments. It is the main alternative to blebs at the leading edge: lamellipodia are driven by actin polymerization, whereas bleb growth is 'pressure-driven' (Charras & Paluch 2008; Diz-Muñoz et al. 2010). First use found: Porter et al. 1973. “ruffles (or lamellipodia) at their free edges”

Also written: lamellipodia, ruffle, leading lamella

See also bleb, pseudopod, lobopodium, mesenchymal–amoeboid transition, Abercrombie steps of migration. Milestones: M13, M18, M19

Laplace's law: The relation between the pressure difference across a curved surface, its tension and its radius of curvature: the smaller the radius, the larger the pressure difference a given tension holds. For membranes it is written T = ΔP·r/2, with T the tension, ΔP the pressure difference and r the radius (Sokabe & Sachs 1990); bleb studies use it to relate cortical tension, intracellular pressure and bleb size (Prothero & Spencer 1968; Tinevez et al. 2009). First use found: Prothero & Spencer 1968. “an equation of the form of LaPlace's law”

Also written: law of Laplace, Laplace equation

See also intracellular pressure, cortical tension, membrane tension. Milestones: M07, M12

large oncosome: A large extracellular vesicle, about 1–10 µm across, shed by amoeboid cancer cells and carrying cancer-promoting (oncogenic) cargo; it is said to come from blebs that pinch off (Di Vizio et al. 2012; Minciacchi et al. 2015). First use found: Di Vizio et al. 2012. “Large Oncosomes in Human Prostate Cancer Tissues”

Also written: oncosome, LO

See also extracellular vesicle, microvesicle, blebbisome, dynamic bleb. Milestones: M17

leader bleb: A single, very large, elongated bleb joined to the cell body by a narrow neck, which leads confined cancer cells migrating without specific adhesion (Logue et al. 2015). Several authors treat it as the same as a stable bleb or the A2 mode (Wu et al. 2018; Ullo & Logue 2018). First use found: Logue et al. 2015. “migrate in the direction of a very large ‘leader bleb.’”

Also written: leader-bleb-based migration, LBBM

See also stable bleb, A1 and A2 amoeboid modes, confinement, constriction ring. Milestones: M20

lobopodium: A blunt, rounded or cylindrical protrusion. The word has two current meanings: an elongated bleb (Charras & Paluch 2008), or a cylindrical protrusion of fibroblasts in 3D matrix that is filled with actin but pushed out mainly by pressure, and is distinct from a bleb (Petrie et al. 2012; García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Holtfreter 1943. “solated and reconstituted each time a lobopodium is formed”

Also written: lobopodia, lobopod, lobopodial migration, lobopodial bleb

See also pseudopod, bleb, lamellipodium, circus movement, intracellular pressure

megakaryocyte budding and proplatelets: Two proposed ways in which megakaryocytes, the large cells that produce platelets, release them: long extensions (proplatelets) that break up, or platelet-sized buds released directly from the cell surface (Potts et al. 2020; Carminita et al. 2024). Those who describe buds do not call them blebs, and studies of mouse marrow disagree on whether buds are platelet precursors (M17). First use found: Wright 1906. “short bud-like pseudopods springing, either directly from giant cells”

Also written: proplatelet, proplatelet formation, membrane budding, megakaryocyte bud, bud-like pseudopod, megakaryocyte bleb

See also microvesicle, bleb, pseudopod. Milestones: M17

membrane tension: The tension of the plasma membrane itself, as distinct from that of the cortex beneath it. It is usually measured by pulling thin membrane tubes (tethers), which gives an apparent tension that also includes membrane–cortex attachment (Dai & Sheetz 1999; Diz-Muñoz et al. 2010). First use found: Prothero & Spencer 1968. “Blebbing has generally been attributed to changes in membrane tension”

Also written: apparent membrane tension, in-plane membrane tension, tether force

See also membrane–cortex attachment, cortical tension, Laplace's law. Milestones: M07, M10, M13

membrane–cortex attachment: The binding of the plasma membrane to the cortex beneath it, through linker proteins such as the ERM proteins. Measured as an energy per unit area by pulling membrane tethers, it opposes bleb formation: in zebrafish cells, weaker attachment gave more and larger blebs (Diz-Muñoz et al. 2010; Bergert et al. 2021). First use found: Dai & Sheetz 1999. “Both membrane-cytoskeleton adhesion and membrane tension contribute to the tether force”

Also written: MCA, membrane-to-cortex attachment, membrane–cytoskeleton adhesion, adhesion energy W0, membrane–cortex linker

See also ERM proteins, rupture vs detachment, membrane tension, cortex, bleb cycle. Milestones: M10, M13, M15

merotomy: Cutting a living cell, usually a protist, into pieces to compare those with and without a nucleus. Pieces without a nucleus kept moving for hours to days but did not regenerate (Nussbaum 1886; Balbiani 1888; Hofer 1889). Historical. First use found: Balbiani 1888. “Par le nom de mérotomie”

Also written: mérotomie (French), künstliche Theilung (German, artificial division), mérozoïte, Splitter (German, splinter), Theilstück (piece)

See also cytoplast, clasmatocyte and clasmatosis, extra-ovate. Milestones: M17

mesenchymal–amoeboid transition: A switch of migrating cells, typically tumor cells in 3D matrix, from an elongated mode that depends on adhesion and proteases (mesenchymal) to a rounded, often blebbing mode (amoeboid). The reverse switch is called AMT (Wolf et al. 2003; Panková et al. 2010). First use found: Wolf et al. 2003. “mesenchymal–amoeboid transition after blocking of pericellular proteolysis”

Also written: MAT, amoeboid–mesenchymal transition (AMT), collective–amoeboid transition, migration plasticity

See also amoeboid, A1 and A2 amoeboid modes, Rho–ROCK, lamellipodium. Milestones: M11, M20

microplast: Albrecht-Buehler's name for tiny fragments of fibroblast cytoplasm, about 2% of the cell volume, made with cytochalasin B; they ruffle or bleb but do not move from place to place (Albrecht-Buehler 1980). First use found: Albrecht-Buehler 1980. “with about 2% of the original cell volume (‘microplasts’)”

Also written: microplasts, independent motile microplast (IMMP)

See also cytoplast, cytokineplast, blebbisome. Milestones: M17

microvesicle: An extracellular vesicle of about 100–1,000 nm that comes from the plasma membrane, unlike exosomes, which are thought to come from the endosomal compartment (Bianco et al. 2009; Minciacchi et al. 2015). 'Microparticle' names the same kind of particle, mostly for vesicles from platelets, endothelial cells and apoptotic cells (Nusbaum et al. 2005); blebs are one proposed source (Di Vizio et al. 2009; Clancy et al. 2015). First use found: Godman et al. 1975. “small bodies (microvesicles or microspherules) of cytoplasmic origin”

Also written: microvesicles, microparticle, microparticles, tumour microparticles, shed vesicles, microspherules, ectosomes

See also extracellular vesicle, large oncosome, apoptotic body, megakaryocyte budding and proplatelets, bleb. Milestones: M08, M17

myosin II: The motor protein that pulls on actin filaments and so contracts the cortex. Its activity, switched on by phosphorylation of its light chain through ROCK or MLCK, generates the cortical tension and pressure that drive blebs (Mills et al. 1998; Charras & Paluch 2008). First use found: Kühne 1864. “den ich von jetzt an Myosin nennen werde”

Also written: non-muscle myosin II, actomyosin, actomyosin contractility, myosin light-chain phosphorylation, Myosin (Kühne)

See also blebbistatin, Rho–ROCK, cortical tension, solation–contraction coupling, cortical contractility. Milestones: M06, M08, M11, M12, M18

nuclear bleb: A bulge of the cell nucleus, where the nuclear envelope protrudes, rather than of the cell surface. One working definition is a protrusion larger than 1 µm with lower DNA density than the rest of the nucleus; nuclear blebs often rupture (Chu et al. 2025). First use found: Gay 1956. “a time at which nuclear membrane blebs also first appeared”

Also written: nuclear blebbing, nuclear herniation, nuclear membrane bleb

See also bleb, hernia, confinement

percolation: In network physics, the point at which enough links have formed for a cross-linked network to span the whole system and transmit force across it. It has been applied to purified actomyosin gels (Alvarado et al. 2013) and to the cortex of stable blebs (García-Arcos et al. 2024, Dev Cell ◆); an older sense is fluid seeping through a porous gel (Cunningham 1995). First use found: Hartwig & Shevlin 1986. “the percolation of solutes and solvents”

Also written: connectivity threshold, critically connected, rigidity percolation, advected percolation, percolation of solvent (fluid sense)

See also active gel, gelation, Flory network theory, poroelasticity, solation–contraction coupling. Milestones: M06, M20

plasmagel and plasmasol: Mast's names for the firm, gel-like outer layer (plasmagel) and the fluid inner cytoplasm (plasmasol) of amoebae; he held that sol turned into gel at the front and gel into sol at the rear (Mast 1923). Now historical. First use found: Mast 1923. “The first I shall designate the plasmasol, the second the plasmagel”

Also written: plasma-gel, plasma-sol, plasmagel sheet, gel/sol ratio

See also plasmalemma, ectoplasm and endoplasm, sol–gel transformation, cortex. Milestones: M04, M05, M06

plasmalemma: Another word for the plasma membrane. Mast used it for the thin, elastic surface layer of amoebae (Mast 1923), and it is still used as a synonym (Babiychuk et al. 2011). First use found: Mast 1923. “the second the plasmagel and the third the plasmalemma”

Also written: plasma membrane, cell membrane, plasmalemmal

See also plasmagel and plasmasol, membrane tension, hyaline layer. Milestones: M04

poroelasticity: A description of the cytoplasm as an elastic, porous solid mesh soaked in fluid. Because a local change in pressure spreads only as fluid flows through the mesh, pressure takes time to even out across the cell (Charras et al. 2005; Moeendarbary et al. 2013). First use found: Charras et al. 2005. “can be described in the framework of poroelasticity”

Also written: poroelastic cytoplasm, fluid-filled sponge

See also intracellular pressure, percolation, cytoplasmic streaming. Milestones: M12

Proteus: The 18th-century name, after the shape-changing sea god, for small freshwater animalcules of no fixed form: Baker's ciliate (1753) and Rösel's 'little Proteus' (1755), later read as an amoeba. The name survives in the species Amoeba proteus (Baker 1753; M01). First use found: Baker 1753. “by the Name of the Proteus”

Also written: den kleinen Proteus (the little Proteus), Volvox proteus, Proteus diffluens, Amiba (Bory), Amoeba proteus

See also amoeboid, pseudopod, sarcode. Milestones: M01, M02

protoplasm: The 19th-century name for the living substance of cells, which with a nucleus was taken to make up the cell (Schultze 1861, 1863). Now mainly historical. First use found: Anonymous 1856. “a nearly-homogeneous mass of ‘protoplasm,’”

Also written: Protoplasma, germinal matter, bioplasm

See also sarcode, amoeboid, ectoplasm and endoplasm, hyaloplasm and granuloplasm. Milestones: M02

pseudopod: A temporary protrusion that an amoeboid cell extends to move or to feed. In current usage it mostly means a protrusion pushed out by actin polymerization, as opposed to a bleb (Charras & Paluch 2008; García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Ehrenberg 1830. “Familia III. PSEUDOPODIA. Corpore proteo, processibus pediformibus variabili”

Also written: pseudopodium, pseudopodia, pseudopode, Scheinfüsse (German), pseudopodial prolongation, Pseudopodia (Latin family name, Ehrenberg 1830)

See also lobopodium, lamellipodium, bleb, amoeboid, pseudopodial wart, cortex scar. Milestones: M02, M04, M09, M18

pseudopodial wart: Ryder's term, used once, for the small blebs he saw along a retracting pseudopod of Amoeba proteus; the same sentence calls them 'blebs' (Ryder 1894). First use found: Ryder 1894. “small blebs or pseudopodial warts”

See also bleb, pseudopod, surface tension theory. Milestones: M03

reconstitution: Rebuilding a cellular process outside the cell from isolated or purified components. For blebs, actin–myosin networks are attached to the inner face of cell-sized lipid vesicles (liposomes), which bleb when the networks contract (Loiseau et al. 2016; Sakamoto & Murrell 2024; Miyazaki et al. 2026). First use found: Taylor et al. 1973. “The chemical control of motility in isolated cytoplasm”

Also written: cell-free model, in vitro reconstitution, minimal cortex, giant unilamellar vesicle (GUV), liposome, cytoskeletal vesicle, actomyosin droplet

See also active gel, cytoplast, rupture vs detachment, solation–contraction coupling. Milestones: M06, M15

Rho–ROCK: The small GTPase RhoA and the kinase it activates, ROCK (Rho kinase). ROCK raises myosin II activity by phosphorylating the myosin light chain and inhibiting its phosphatase; this is the best-studied signaling route to the contractility that drives blebs (Mills et al. 1998; Sahai & Marshall 2003). First use found: Mills et al. 1998. “Rho also stimulates Rho kinase (ROK)”

Also written: ROCK, ROCK I, Rho kinase, ROK, RhoA–ROCK axis

See also myosin II, blebbistatin, mesenchymal–amoeboid transition, apoptotic bleb. Milestones: M11, M18

rupture vs detachment: The two proposed ways a bleb can start: the membrane comes away from an intact cortex (detachment), or the cortex itself tears (rupture) (Tinevez et al. 2009). Both routes have been reproduced in liposomes, where actin–membrane coupling and cross-linking decide which one occurs (Miyazaki et al. 2026). First use found: Ryder 1894. “a sudden rupture occurs through which a fresh outpour”

Also written: cortex rupture, cortical breakage, tearing, delamination, membrane–cortex detachment, bleb nucleation

See also bleb cycle, membrane–cortex attachment, cortex, percolation. Milestones: M04, M08, M10, M12, M15

sarcode: Dujardin's name (1835) for the clear, jelly-like, contractile living substance of simple animals, later identified with protoplasm (Schultze 1863). Now historical. First use found: Dujardin 1835. “cette matière diaphane glutineuse que j'appellerai sarcode”

Also written: Sarkode (German), gelée vivante (living jelly)

See also protoplasm, sol–gel transformation, amoeboid. Milestones: M02, M06

septin signaling hub: Assemblies of curvature-sensing septin proteins that gather at the curved bases of dynamic blebs and scaffold NRAS and its downstream kinases. Through them, blebbing keeps ERK and PI3K survival signaling active in melanoma cells that have lost their attachment (Weems et al. 2023). First use found: Weems et al. 2021 preprint. “recruit curvature sensing septin proteins”

Also written: bleb-associated septin structures, bleb signalling, bleb-induced survival signalling, septin signalling hub

See also dynamic bleb, bleb, mesenchymal–amoeboid transition. Milestones: M16

solation–contraction coupling: The hypothesis that a cross-linked actin gel resists contraction, so that myosin can slide filaments and contract the network only where cross-links are loosened locally and in a regulated way (solation) (Hellewell & Taylor 1979; Janson & Taylor 1993). Its role in amoeboid cytoplasm is proposed (M06). First use found: Hellewell & Taylor 1979. “The solation-contraction coupling hypothesis”

Also written: solation-contraction coupling hypothesis, gelation-solation-contraction cycle

See also sol–gel transformation, gelation, Flory network theory, percolation, active gel. Milestones: M06

sol–gel transformation: The idea that cytoplasm switches back and forth between a fluid state (sol) and a solid-like state (gel). From the 1910s to the 1970s it was used to explain how pseudopods form and how the tail contracts (Mast 1923; de Bruyn 1947); in molecular terms it corresponds to the cross-linking and loosening of actin networks (Pollard & Ito 1970; Taylor et al. 1973). First use found: Mast 1923. “solation and gelation have been suggested as factors in locomotion”

Also written: sol-gel theory, gelation–solation, gel/sol ratio

See also plasmagel and plasmasol, gelation, solation–contraction coupling, percolation. Milestones: M04, M05, M06

stable bleb: A large bleb that lasts for up to hours and may hold most of the cytoplasm and the nucleus. It leads confined or highly contractile cells in stable-bleb (A2, leader-bleb) migration: its cortex flows rearwards, which keeps the bleb tip free of actin and hinders retraction (Liu et al. 2015; Ruprecht et al. 2015; García-Arcos et al. 2024, Trends Cell Biol ◆). First use found: Cunningham 1995. “from the surface of a stable bleb”

Also written: stable-bleb migration, stable-bleb cell, large stable bleb

See also leader bleb, A1 and A2 amoeboid modes, blebbing regimes, confinement, cortical flow. Milestones: M10, M20

surface tension theory: The 19th- and early 20th-century explanation of amoeboid movement that treated the cell as a liquid drop, which moves by a local fall in its surface tension (Berthold, Bütschli and Rhumbler, as cited by Mast 1923). It was abandoned by the 1940s (de Bruyn 1947). First use found: Verworn 1892. “dass an der betreffenden Stelle der Peripherie die Oberflächenspannung vermindert wird”

Also written: surface-tension theory of amoeboid movement

See also cortical tension, pseudopodial wart, sol–gel transformation. Milestones: M03, M04, M07

tail contraction and frontal contraction: Two rival accounts of where force is generated in large amoebae: either the outer ectoplasmic tube contracts at the tail and pushes the endoplasm forward, or contraction at the front, in the 'fountain zone', pulls it (Allen & Cowden 1962; Taylor et al. 1973). First use found: Allen & Cowden 1962. “The ectoplasmic contraction theory (or tail contraction theory)”

Also written: ectoplasmic contraction theory, tail contraction theory, frontal contraction theory, fountain zone, fountain streaming

See also hyaline cap, cortical flow, plasmagel and plasmasol, solation–contraction coupling, cytoplasmic streaming. Milestones: M04, M05, M06

uropod: The tail at the rear of a migrating leukocyte or other amoeboid cell (Haston et al. 1982). Confined A2 cells have one, which is dragged along and slows them (Liu et al. 2015). First use found: Skinnider et al. 1977. “the occasional uropod seen, which was single”

Also written: tail, uropodium

See also constriction ring, A1 and A2 amoeboid modes, amoeboid, friction (active and passive). Milestones: M09, M20

zeiosis: An obsolete word for repeated blebbing, likened by its coiners to a thick fluid boiling. Costero & Pomerat (1951) coined it for stalked blebs that formed and vanished along the dendrites of cultured neurons; it was then used for rapid, repeated projection and retraction of blebs and for drug-induced knobs of endoplasm (Price 1967; Godman et al. 1975). First use found: Costero & Pomerat 1951. “we refer to this phenomenon as zeiosis”

Also written: zeiotic bleb, zeiotic blebbing, knobbing

See also bleb, bubble, blister, hernia. Milestones: M03, M08, M17